Sufficiently high bioavailability and, as a consequence, therapeutic efficacy of peptides is frequently ensured only by parenteral administration, because peptides undergo proteolytic degradation after oral administration, only low absorption takes place nasally, and no absorption takes place dermally. Because of the low half-life of peptides in the body, parenteral administration of peptide medicaments, e.g. luteinizing hormone releasing hormone (LHRH) analogs such as the so-called superagonists, for example goserelin (INN), leuprorelin (INN) or triptorelin (INN), and LHRH antagonists such as, for example, antide (INN), cetrorelix (INN), degarelix (INN) or ganirelix (INN), must take place each day within a therapy period in order to achieve and maintain the desired suppressant effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
The result of this suppression in men is the reduction in the production and release of testosterone and in women there is a reduction in the production and release of estradiol, it being perfectly possible for the degree of reduction required to vary between the medical indications. Lowering the blood levels of sex hormones is a standard therapy in the palliative treatment of sex hormone-sensitive tumors, for which a permanent reduction to a low level (castration) is necessary. It is also standard therapy for the treatment of benign gynecological or urological disorders, e.g. endometriosis, uterine leiomyomas, uterine fibroids and benign prostate hyperplasia (BPH), for the treatment of fertility impairments and for contraception, it also being possible in these cases, depending on the therapeutic strategy, for intermittent partial reduction of the sex hormone levels to be sufficient.
The need for depot formulations which can be administered parenterally for long-lasting and controlled release of peptide medicaments, making the need for daily administrations obsolete, was recognised a relatively long time ago.
DE 38 22 459 A1 discloses pharmaceutical formulations which comprise complexes of water-insoluble peptides, such as, for example, LHRH analogs, with embonic, tannic and stearic acid and biodegradable lactic acid-glycol acid copolymers. In the production process disclosed therein, chlorinated hydrocarbons such as dichloromethane are employed as solvents and subsequently removed for the most part by rotary evaporation. However, the use of such potentially carcinogenic solvents is disadvantageous because of the high residual solvent content, e.g. ˜4500 ppm dichloromethane (Koushik K and Kompella U B, Pharmaceutical Research, 2004, 21: 524-535), in pharmaceutical forms produced by solvent evaporation. The ICH guideline “Impurities: Guideline for Residual Solvents—Q3C” strictly limits the residual solvent content for class 2 solvents in pharmaceutical products for reasons of drug safety, e.g. for the chlorinated hydrocarbons dichloromethane and chloroform to respectively 600 ppm and as low as 60 ppm. A further crucial disadvantage is the rotary evaporation of the volatile toxic solvent because of the risk of contamination and explosion. Use of chlorinated hydrocarbons in the production process additionally represents a hazard for employees and the environment. Sterility of the pharmaceutical formulations is achieved only by a subsequent gamma irradiation. Besides the aspects of considerable additional costs and increased potential hazards for employees and the environment, subsequent gamma irradiation also leads however, because of the higher radiation dose (25 kGy according to Ph. Eur.), to increased decomposition and therefore has a disadvantageous effect on the stability of such formulations. In addition, the use of gamma irradiation represents a particular obstacle to authorization with elaborate qualification and validation requirements (see: EC Guide to Good Manufacturing Practice—Annex 12).
U.S. Pat. No. 5,134,122 describes the production of microparticles of a lactic acid-glycolic acid copolymer which comprise, as pharmaceutically active substance, peptides in the form of their water-insoluble embonate, tannate, stearate or palmitate salts. However, the process described therein requires the disadvantageous use of special elaborate extrusion machines and a thermal treatment at up to 100° C., which may lead to destruction of the peptides and to a greater level of contamination of the pharmaceutical form by increased degradation or condensation products. A further disadvantage of the process is the need to sieve the microparticles in order to obtain the desired particle size. Such a sieving step is scarcely possible in an aseptic production process in a clean room because of the potential particle contamination (see: EC Guide to good Manufacturing Practice—Annex 1).
DE 42 23 282 A1 and DE 42 23 284 A1 (and U.S. Pat. No. 5,445,832 and U.S. Pat. No. 5,637,568 as US patents belonging to the patent family) describe processes for producing pharmaceutical preparations in which water-insoluble medicamentous peptide substances are incorporated into microparticles of a biodegradable polymeric material. Both processes have the already described disadvantage of the obligatory use of carcinogenic chlorinated hydrocarbons and the problem of physiologically unacceptable residual solvent contents. A further disadvantage is the low percentage loading of the microparticles with active ingredient, and the already discussed gamma irradiation.
DE 43 42 092 A1 (and U.S. Pat. No. 5,773,032 as US patent belonging to the patent family) discloses the nonsterile production of slightly soluble salts of peptide LHRH analogs by reacting an aqueous solution of the acid salt with an acetic acid solution of the LHRH analog base to precipitate the slightly soluble acid addition salt, and the use thereof as medicaments. One disadvantage of this process is, however, the obligatory filtration step which, on the pilot and production scale, on use of, for example, 30 g of peptide in the batch, leads to the formation of inhomogeneous gelatinous peptide precipitates which cannot be resuspended and cause intolerable long filtration times. In addition, the filtration is associated with a disadvantageous coprecipitation of alkaline earth metal and alkali metal salts, such as, for example, sodium acetate, which may promote decomposition of the peptide salt, and may lead to tolerability problems occurring in patients on parenteral administration. Further disadvantages of this production process are the use of organic solvents such as dimethylacetamide and dimethyl acetate, with the already described problem of the residual solvent content, and the necessary sieving step which is scarcely possible, as already mentioned above, on aseptic production in a clean room. In addition, the salts and suspensions described in DE 43 42 092 A1 and produced by the disclosed process are not sterile, because the process described therein and including the process steps of ‘filtration’ and ‘drying’ cannot industrially result in intrinsically sterile process products (there: dried filter cake as precipitate), thus making for example direct parenteral administration, but also further processing in an aseptic process, impossible.
The lacking sterility, which is an obligatory requirement for aseptic further processing and administration of such salts and suspensions as medicaments, could be achieved only by an additional sterilization step, which is not disclosed in DE 43 42 092 A1, by gamma irradiation.
As already discussed above, however, subsequent gamma irradiation leads, because of the high radiation dose, to an increased decomposition and therefore has disadvantageous effects on the stability of such salts and suspensions, besides the aspects of considerable additional costs, increased potential hazards for employees and the environment and elaborate qualification and validation measures. In addition, the salts produced according to DE 43 42 092 A1 are in the form of microparticles with which it is not possible to generate suspensions which are stable for a prolonged period without, or even with, addition of additives which increase the viscosity and assist resuspendability. Although it is possible to generate a suspension, e.g. in aqueous solution, with continuous mixing, it corresponds rather to an agitation of the solid microparticles in the liquid phase. If the mixing is stopped or interrupted, a two-phase mixture quickly forms again and consists of solid phase (microparticles) and liquid phase (aqueous solution) separate from one another.
Felberbaum et al. (Human Reproduction, 1998, 13: 1660-1668) describe the use of the cetrorelix embonate microparticles produced according to DE 43 42 092 A1 in the treatment of uterine fibromas. A sterile suspension of the microparticles treated by gamma irradiation, in which the microparticles were resuspended in an aqueous solution with the addition of polysorbate 80, sodium hydroxide solution and carboxymethylcellulose (CMC), was employed. However, as already indicated above, such a formulation of cetrorelix embonate microparticles does not represent a suspension which is stable for a prolonged period even with addition of additives which increase the viscosity and assist resuspendability; on the contrary it quickly separates again to a two-phase mixture composed of liquid and solid phase separate from one another.
Additionally, however, the addition of viscosity-increasing CMC represents a considerable disadvantage because CMC may lead, especially on parenteral administration, to allergic reactions or even anaphylaxis (Bigliardi et al., Dermatology 2003, 207:100-103; Oppliger and Hauser, JDDG 2004, 2:928-930), and should therefore be avoided. Furthermore, administration of the microparticle suspension led to inadequate estradiol suppression in some patients. On the other hand, in other patients there was a reduction in the estradiol level to distinctly below 20 pg/ml and thus an unwanted chemical castration (see also: Kaufmann et al., Journal of Clinical Oncology 1989, 7: 1113-1119; Battaglia et al., Gynecological Endocrinology 1995, 9: 143-148; Reron et al., Neuroendocrinology Letters 2002, 23: 455-458) with the corresponding hormone withdrawal manifestations which are disadvantageous for the patients. The authors themselves speak of the need for an improved formulation which avoids the observed disadvantages.
DE 100 40 700 A1 (and U.S. Pat. No. 6,780,972, US 2002/198146 and US 2004/259801 as US patents belonging to the patent family) describes a process for producing slightly soluble peptide salts, in which the dissolved initial peptide salt of a basic peptide is reacted with a mixed bed ion exchanger or a mixture of an acidic and basic ion exchanger to form the free basic peptide, subsequently the ion exchanger is removed, the free basic peptide is reacted with an acid to form the final peptide salt, and finally the solvent is removed. The process disclosed therein has the disadvantage, however, that nonsterile ion exchangers not complying with GMP guidelines must be used and represent, because of organic residues such as sulfonic acid residues and microbiological residues, a potential source of contamination. Thus, the microbiological load of the inner cavities of the nonsterile ion exchanger particles cannot be ascertained straightforwardly before use. The use of such ion exchangers represents an unacceptable and unpredictable risk of contamination of the peptide complexes to be prepared because of possible mechanical damage or possible destruction of the particles during the reaction process, such as, for example, by stirring or shaking. A further disadvantage is the instability of the free peptide base in basic solution, which leads to increased decomposition products in only a short time, e.g. after only 10 minutes, which would according to the ICH guideline “Impurities in New Drug Products—Q3B(R)” make elaborate identification and qualification measures necessary for the suspensions disclosed in the patent. This disadvantageous decomposition can only partly be counteracted by a large molar excess of ion exchanger, which in turn entails the disadvantage of lower product yields (approx. 15-20% loss of yield) in the reaction. A further disadvantage of the disclosed process is the increased thermal stress on the slightly soluble peptide salts due to the need to remove the solvent by distillation, which likewise leads to increased decomposition products and thus a greater degree of contamination in the pharmaceutical form. In addition, removal of volatile solvents by distillation is scarcely possible in a clean room area because of the risk of contamination and explosion. Moreover, the suspensions produced by the disclosed process are not necessarily sterile and may even, for the reasons mentioned above, be microbiologically contaminated. With sparingly soluble peptide salts prepared by the process of DE 100 40 700 A1 there is accordingly always a need before use for parenteral administration that they be sterilized, for example by gamma irradiation, which is associated with the disadvantages already described.